Here is a new twist to a familiar type of roadbed construction. Indoor modelers have long used splines cut from wood, masonite, or Homosote to fabricate sturdy roadbed. Splines provide strength, good transition curves, and excellent sound deadening qualities. On the downside, they are labor intensive and time consuming to build correctly and may require stabilization to handle humidity and temperature variations. They also tend to deteriorate rapidly when used in an outdoor environment.
I build my spline roadbed for my indoor Sn3 layout with pine lattice or with home-made strips cut on a table saw from redwood or cedar. I had planned on using the same technique for my new Fn3 outdoor layout. Lately, the price of wood has made this type of construction less attractive. I figured there must be a cheaper and better way to solve the problem.
After completing a recent lawn sprinkler installation project, I had several left-over pieces of ½” and ¾” diameter PVC pipe. As I was lifting a length of pipe into the rafters for storage, I noticed that it curved gracefully in a wide arc. I thought to myself, “What a smooth transition curve.” Eureka … the light went on! After a brief bit of experimenting, I came up with a couple of interesting spline roadbed arrangements.
The following examples were all fabricated from Schedule 40 PVC pipe. This pipe is fairly rigid, but can be curved for radii down to about 8 feet for Fn3. To form tighter radii you can substitute a thinner walled PVC pipe, such as Schedule 125 or Schedule 200. You can also use other types of plastic pipe such as PEX. I have not yet done any experimenting with PEX pipes, but the construction techniques used should be about the same as those described for the PVC.
PVC and PEX pipe are available at most home improvement stores (Lowes, Home Depot, etc.) PVC pipe comes in 10-foot and 20-foot lengths. PEX pipe is available in 5-foot or 10 foot lengths, and also in 50-foot and 100-foot coils, depending on diameter. If you decide to use PEX, select diameters that are approximately the same external size of the ¾” PVC used in these examples.
These examples do not include diverging splines (for turnouts.) To construct diverging splines, use the same technique as for wooden splines. Simply spread the outer splines to the required divergence angle and add additional splines to each diverging route as clearance is available.
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The Fn3 roadbed for outdoor use is made from three adjacent splines of ¾” PVC pipe. I have developed two different arrangements for the roadbed. The first method uses three adjacent splines of ¾” PVC pipe as shown in Figure 1. The pipes are place side by side, touching each other, with staggered end joints.
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End joints are not connected. The three adjacent pipes are connected to each other with 2-inch long deck screws inserted from alternate sides at approximately 12-inch intervals. “Liquid Nails” construction adhesive is liberally applied to the top of each pipe and allowed to fill the “V” gaps between the pipes. Wood ties are laid on the tops of the pipes into the wet adhesive. Rail is spiked to the ties after the adhesive is cured.
The roadbed is placed directly on the ground or supported by bricks as needed. This method of roadbed construction seems to work best for garden layouts where the track is laid at approximate ground level and where severe weather is not a problem.
The second method shown in Figure 2 is a bit more complicated, but it provides maximum strength. It also uses three splines of ¾” PVC pipe. The three pipes are arranged in a triangular cross-section. The two upper pipes have staggered end joints connected with ¾” PVC “COUPLING” fittings using PVC pipe glue.
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The pair of upper pipes rest on a lower pipe made from approximate 5-foot lengths of ¾” pipe. The 5-foot sections are joined with PVC “TEE” fittings using PVC pipe glue. Variable length risers are made from scrap lengths of ¾” PVC pipe and extend vertically from each “TEE” fitting downward approximately 12 inches below ground level. The three splines do not touch each other except at “COUPLING” and “TEE” fittings. At all other points, there is a gap of approximately 1/8” between the three pipes.
I install the lower spline and vertical risers first. Then I assemble the upper splines and temporarily attach them to the lower spline with string or nylon cable ties. When the grades, curvatures, and general alignments are correct, I fill the gaps between the splines with expanding foam insulation. After twenty-four hours, this insulation is cured and will hold the splines in the desired position. After sanding or scraping the top surface flat, I attach either wooden ties for handlaid track or flex track with polyurethane glue or construction adhesive.
This method of roadbed construction seems to work best for garden layouts on uneven terrain. It is ideal for extended lengths of track above grade level, or for garden layouts in areas where winter frost heaves wreck havoc with conventional track laying methods.
PVC pipe is light-weight, strong, inexpensive, readily available, and easy to assemble. It is impervious to changes in temperature and humidy. PVC can be placed safely on or in the ground without worry about rot or termites. In addition, PVC pipe offers a nice feature not available with traditional spline construction – with Method 2 you can route electrical wiring through the splines just like electrical conduit. (I use battery power and DCC radio control, so I don’t have any wiring to worry about.) I urge you to give PVC pipe splines a try – you may never go back to wood again!
Bob "Sn3nut" Hyman
I build my spline roadbed for my indoor Sn3 layout with pine lattice or with home-made strips cut on a table saw from redwood or cedar. I had planned on using the same technique for my new Fn3 outdoor layout. Lately, the price of wood has made this type of construction less attractive. I figured there must be a cheaper and better way to solve the problem.
After completing a recent lawn sprinkler installation project, I had several left-over pieces of ½” and ¾” diameter PVC pipe. As I was lifting a length of pipe into the rafters for storage, I noticed that it curved gracefully in a wide arc. I thought to myself, “What a smooth transition curve.” Eureka … the light went on! After a brief bit of experimenting, I came up with a couple of interesting spline roadbed arrangements.
The following examples were all fabricated from Schedule 40 PVC pipe. This pipe is fairly rigid, but can be curved for radii down to about 8 feet for Fn3. To form tighter radii you can substitute a thinner walled PVC pipe, such as Schedule 125 or Schedule 200. You can also use other types of plastic pipe such as PEX. I have not yet done any experimenting with PEX pipes, but the construction techniques used should be about the same as those described for the PVC.
PVC and PEX pipe are available at most home improvement stores (Lowes, Home Depot, etc.) PVC pipe comes in 10-foot and 20-foot lengths. PEX pipe is available in 5-foot or 10 foot lengths, and also in 50-foot and 100-foot coils, depending on diameter. If you decide to use PEX, select diameters that are approximately the same external size of the ¾” PVC used in these examples.
These examples do not include diverging splines (for turnouts.) To construct diverging splines, use the same technique as for wooden splines. Simply spread the outer splines to the required divergence angle and add additional splines to each diverging route as clearance is available.
[/b]
The Fn3 roadbed for outdoor use is made from three adjacent splines of ¾” PVC pipe. I have developed two different arrangements for the roadbed. The first method uses three adjacent splines of ¾” PVC pipe as shown in Figure 1. The pipes are place side by side, touching each other, with staggered end joints.
End joints are not connected. The three adjacent pipes are connected to each other with 2-inch long deck screws inserted from alternate sides at approximately 12-inch intervals. “Liquid Nails” construction adhesive is liberally applied to the top of each pipe and allowed to fill the “V” gaps between the pipes. Wood ties are laid on the tops of the pipes into the wet adhesive. Rail is spiked to the ties after the adhesive is cured.
The roadbed is placed directly on the ground or supported by bricks as needed. This method of roadbed construction seems to work best for garden layouts where the track is laid at approximate ground level and where severe weather is not a problem.
The second method shown in Figure 2 is a bit more complicated, but it provides maximum strength. It also uses three splines of ¾” PVC pipe. The three pipes are arranged in a triangular cross-section. The two upper pipes have staggered end joints connected with ¾” PVC “COUPLING” fittings using PVC pipe glue.
The pair of upper pipes rest on a lower pipe made from approximate 5-foot lengths of ¾” pipe. The 5-foot sections are joined with PVC “TEE” fittings using PVC pipe glue. Variable length risers are made from scrap lengths of ¾” PVC pipe and extend vertically from each “TEE” fitting downward approximately 12 inches below ground level. The three splines do not touch each other except at “COUPLING” and “TEE” fittings. At all other points, there is a gap of approximately 1/8” between the three pipes.
I install the lower spline and vertical risers first. Then I assemble the upper splines and temporarily attach them to the lower spline with string or nylon cable ties. When the grades, curvatures, and general alignments are correct, I fill the gaps between the splines with expanding foam insulation. After twenty-four hours, this insulation is cured and will hold the splines in the desired position. After sanding or scraping the top surface flat, I attach either wooden ties for handlaid track or flex track with polyurethane glue or construction adhesive.
This method of roadbed construction seems to work best for garden layouts on uneven terrain. It is ideal for extended lengths of track above grade level, or for garden layouts in areas where winter frost heaves wreck havoc with conventional track laying methods.
PVC pipe is light-weight, strong, inexpensive, readily available, and easy to assemble. It is impervious to changes in temperature and humidy. PVC can be placed safely on or in the ground without worry about rot or termites. In addition, PVC pipe offers a nice feature not available with traditional spline construction – with Method 2 you can route electrical wiring through the splines just like electrical conduit. (I use battery power and DCC radio control, so I don’t have any wiring to worry about.) I urge you to give PVC pipe splines a try – you may never go back to wood again!
Bob "Sn3nut" Hyman
